Methods of manufacturing shell moulds

ABSTRACT

Method of manufacturing shell moulds wherein each disposable mould comprises a central core frame secured to an operating head utilized for immersing the pattern in succession into vessels containing alternately refractory slip and refractory grains in the form of fluidized suspension, respectively, said central core frame revolving automatically about the vertical axis of a turnstile adapted, through an intermittent rotation, to bring in succession said head above the vessels, about another axis of said core frame and finally about an axis perpendicular to said core frame axis for performing a limited pivotal movement sufficient however for immersing the pattern into each vessel and removing it therefrom during the pauses produced in the rotation of said turnstile, this method applying more particularly to precision foundry processes.

I Jan. 29, 1974 United States Patent [191 Jasson et al.

[ METHODS OF MANUFACTURING SHELL MOULDS Primary ExaminerJ. Spencer Overholser Assistant ExaminerJohn E. Roethel [75] Inventors: Philippe Jasson; Pierre Chatourel,

Attorney, Agent, or Firm steven's. Davis. Miller & Mosher both of Billancourt, France [73] Assignee: Regie Nationale Des Usines Renault,

Billancourt, France [57] ABSTRACT Method of manufacturing shell moulds wherein each disposable mould comprises a central core frame secured to an operating head utilized for immersing the pattern in succession into vessels containing alternately refractory slip and refractory grains in the form of fluidized suspension, respectively, said central core frame revolving automatically about the vertical axis of a turnstile adapted, through an intermittent rotation, to bring in succession said head above the vessels, about another axis of said core frame and finally about an axis perpendicular to said core frame axis for O0 1 M. an

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PATENTEUJANZS m4 3.788.380

sum 1 [1F METHODS OF MANUFACTURING SHELL MOULDS This invention relates in general to the manufacture of shell moulds of the type utilized in lost-pattern precision foundry processes and has specific reference to an improved method of manufacturing lost-pattem shell moulds for use in precision foundry.

In this method, each disposable pattern or cluster of patterns comprises a central or core frame secured to an operating head utilized for immersing the pattern or cluster of patterns in succession into vessels filled alternately with liquid refractory slip immersion and refractory grains in fluidized suspension, respectively.

The successive layers obtained by immersing the pattern or patterns into the slip and dusting said pattern or patterns with refractory grains, in conjunction with the hardening of these layers as a consequence of the drying thereof or of the chemical reactions produced therebetween, provide on these patterns a shell of refractory material which, after the remove] of said patterns, will constitute the mould proper.

However, the fragility of the lost patterns, consisting as a rule of hard, brittle materials, constituted heretofore a chief obstacle in preventing a complete automation and mechanization of these mould immersion and dusting operations, together with the necessity of obtaining layers having a thickness as uniform as possible through proper handling of said moulds in combination with a constant visual checking of the distribution of the refractory products over their surface.

On the other hand, the production rate as well as the quality and reproductibility of the operations are lim ited considerably by this manual process, due to importance of the human factor thus involved.

On the other hand, the clusters of patterns, due to their considerably weight when the very first layers have been applied thereto, are held in a vertical suspended condition by the operators during their immersion into the slip-containing vessels or into the fluidized beds used for dusting the patterns with refractory grains. As a result, the liquid deposits constitute layers that are thicker at the lower ends than near the handling supports, and conversely, as a consequence of a greater erosion effect, the grain layers are thinner at the ends than near the handles.

Notwithstanding a less static handling involving skilled movements such as vertical turning (i.e., upsidedown) and alternate rotational movements of the clusters about their axis by means of a corresponding rotation of the operators wrist, with a view to obtain the maximum permissible uniformity of the thickness of the above-defined layers, these remain rather heterogeneous. Moreover, these repeated handling constitute very tiresome operations, in spite of the possible use of mechanical handling equipments, such as balancing apparatus, but this constitutes an additional cause of irregularity in the mould forming process.

Now these mould irregularities are a primary cause of casting rejection, due notably to the breakage of moulds during the casting operation or during the handling thereof, or alternately as a consequence of casting defects due to variations in their setting conditions resulting from variations in the mould thickness.

lt is the chief object of the present invention to avoid the inconveniences set forth hereinabove by imparting to the moulds, through fully mechanical means, a combination of movements of rotation producing the immersion thereof into slip-containing baths and into fluidized beds.

While being of the type mentioned in the preamble of this specification, the method constituting the subject-matter of the present invention is characterized in that the core frame is caused to revolve automatically about three axes of rotation, i.e., a first axis of rotation constituting the vertical axis of a tumstile adapted, by an intermittent rotational movement, to bring the operative head in succession above the various vessels; a second axis of continuous rotation, substantially coincident with the axis of said core frame, and a third axis of rotation, perpendicular to said second axis, which passes through the center of a circumference to which said second axis is tangent, the core frame lying externally of said circumference, while the rotation about said third axis consists of an angularly limited pivotal movement sufficient however for immersing into, and removing from, each vessel, the pattern or cluster of patterns during the pauses occurring during the rotational movement of said turnstile.

As a result of this combination of rotational movements, i.e., rotation of the mould about its axis, added to a rotation about a horizontal axis perpendicular to the mould axis and not intersecting this axis, the mould is caused to penetrate into and emerge from the slip bath vessels and fluidized bed vessels with a sweeping movement which is both axial and rotational, according to constantly variable mould inclinations, thus ensuring a uniform distribution of the products over the mould surface. The upper position of the mould corresponds to its dripping position and also to its transfer from one vessel to another.

Advantageously, the pivotal movement may take place between the immersion position during which the core frame is directed downwards, while the second axis is substantially vertical, and the dripping position during which the core frame is inclined obliquely upwards, the angle of sweep of this frame being inferior to According to a typical form of embodiment of the method of this invention, the patterns are secured to the operating heads by fitting their central tubular member on a fastening rod locking said frame in position, as a consequence of the inflation of deformable bearing surfaces expansible by virtue of the permanent action of resilient means, a suitable compensation of these resilient means permitting the release of the expansible bearings and the disassembling of the moulds formed on the patterns.

An additional and valuable feature of the combination according to this invention of simple rotational movements is its great facility of construction by resorting to mechanical element driven from hydraulic means, according to a preferred form of embodiment of the invention. The high flexibility and easy adjustment characteristics of hydraulic control systems af ford extremely sensitive adjustments consistent with the mould fragility. Furthermore, the various rotational speeds, of the different movements may easily be adjusted and varied according to a predetermined programme.

The complete automatism thus obtained in the moulding operations, in conjunction with the combination of immersion and dripping movements according to this invention, are conductive to a quality and uniformity of the mould shells that were hitherto unattainable with manual processes, and furthermore this automatism afford production rates consistent with the highest possible industrial series.

Of course, the method of this invention may be carried out by using any suitable installation comprising a turnstile having disposed in radial relationship thereto the various vessels and comprising rotary and pivoting supports for the patterns, the necessary synchronism of the various movements being obtained, for example, by using toothed gears and/or motors responsive to limit switches or like control means.

A typical form of embodiment of the method of this invention will now be described with reference to the accompanying drawing illustrating diagrammatically by way of example a four-station installation comprising two immersion stations and two fluidized-bed dusting stations, disposed inalternate relationship along a circumference. In the drawing:

FIG. 1 is a general perspective view of the apparatus comprising a four-station turnstile according to this preferred form of embodiment; and

FIG. 2 is an elevational view of a mould handling head, during the mould making process, showing the various positions assumed by said mould.

The structure shown in FIG. 1 comprises four operating heads I mounted on a central turnstile 2 surrounded by vessels 3 containing fluidized beds, alternating with other vessels 4 containing immersion products, this assembly being adapted to be supported by a common base 5. Mounted to the rotary platform of turnstile 2 are frames 6 supporting the aforesaid operating heads 1. This platform is adapted, by successive angular movements through 90 about a first vertical central axis 7, to transfer the clusters 8 of patterns and the operating heads 1 from one working station to another, where this platform is locked during the cluster immersion operations.

These clusters are secured to the operating heads 1 by engaging or fitting their central tubular frames 9 to the fastening rod 11 provided with clamping bearing surfaces adapted to be expanded by compressing deformable bearings consisting for example of rubber rings constantly kept in a compressed condition when inoperative (non-activated controls) by resilient means 12 (FIG. 2) incorporated in the spindle of head 1.

The control or operating heads 1 are adapted to impress to the moulds 8 being formed a continuous rotational movement about a second axis 13 corresponding to their mounting axis, and also a partial rotation through an angle a (FIG. 2) about a third horizontal axis 14 perpendicular to said axis 13 and somewhat offset in relation thereto. This partial rotation brings the mould 8 to a substantially vertical position as shown at 8 in FIG. 2, so that it is immersed completely in the corresponding immersion or dusting vessel, after having caused its gradual penetration with a downward movement attended by a rotation and a constant change in its inclination. Then the mould is brought back, by reversing its rotation through the angle a, to the reverse oblique upper position 8 in which the excess liquid or grains are dripped off before the assembly is moved again through one-fourth of a revolution above the next vessel.

By properly varying the waiting periods or pauses and the travel speeds, as well as the number of sequences corresponding to the number of layers applied to the moulds, the method may be adapted to different mould types and thus the immersion programme corresponding to the best possible operating conditions may be obtained in a reproductible manner and with all the flexibility afforded by the use of hydraulic control and/or driving means.

The technical structure of the control and driving means, notably for a turnstile machine 2 controlling the rotational movements according to the method of this invention, is disclosed in a co-pending patent application in the name of the same applicant.

What I claim as new is:

1. Method of manufacturing shell moulds of the lostpattern type for precision moulding processes, wherein each disposable pattern or pattern cluster comprises a central core frame secured to a control or operating head adapted to immerse the pattern or pattern cluster successively into a vessel containing liquid refractory slip and into a vessel containing refractory grains in the form of a fluidized suspension, and in which said core frame is caused to rotate automatically about three axes of rotation of which the first axis is the vertical axis of a turnstile adapted through an intermittent rotational movement to bring said operating head in succession above said vessels, the second axis of continuous rotation being substantially coincident with that of said core frame, and the third axis of rotation being a horizontal axis which is perpendicular to said second axis, which intersects said first axis and which passes through the center of a circumference to which said second axis is tangent, said core frame being disposed externally of said circumference, the rotation about said third axis consisting of an angularly limited pivotal movement, said pivotal movement taking place during each pause in the rotation of said turnstile between an immersion position in which said core frame is directed down-wards, the second axis being then substantially vertical, and a dripping position in which said frame is directed obliquely upwards, the angle swept by said frame being less than 180 but more than and wherein the patterns are secured to the operating heads by fitting their tubular central core to a fastening rod which locks said frame in the selected position by diametrically inflating deformable bearing surfaces which are adapted to expand under the permanent axial action of resilient means and with compensating means for said resilient means to permit the release of the expansible bearing surfaces and the removal of the moulds formed on said patterns.

2. Method according to claim 1, wherein the numbers, amplitudes and speeds of the various movements accomplished by the patterns are adjustable and are obtained by using suitable programmed hydraulic control and driving means. 

1. Method of manufacturing shell moulds of the lost-pattern type for precision moulding processes, wherein each disposable pattern or pattern cluster comprises a central core frame secured to a control or operating head adapted to immerse the pattern or pattern cluster successively into a vessel containing liquid refractory slip and into a vessel containing refractory grains in the form of a fluidized suspension, and in which said core frame is caused to rotate automatically about three axes of rotation of which the first axis is the vertical axis of a turnstile adapted through an intermittent rotational movement to bring said operating head in succession above said vessels, the second axis of continuous rotation being substantially coincident with that of said core frame, and the third axis of rotation being a horizontal axis which is perpendicular to said second axis, which intersects said first axis and which passes through the center of a circumference to which said second axis is tangent, said core frame being disposed externally of said circumference, the rotation about said third axis consisting of an angularly limited pivotal movement, said pivotal movement taking place during each pause in the rotation of said turnstile between an immersion position in which said core frame is directed down-wards, the second axis being then substantially vertical, and a dripping position in which said frame is directed obliquely upwards, the angle swept by said frame being less than 180* but more than 90* and wherein the patterns are secured to the operating heads by fitting their tubular central core to a fastening rod which locks said frame in the selected position by diametrically inflating deformable bearing surfaces which are adapted to expand under the permanent axial action of resilient means and with compensating means for said resilient means to permit the release of the expansible bearing surfaces and the removal of the moulds formed on said patterns.
 2. Method according to claim 1, wherein the numbers, amplitudes and speeds of the various movements accomplished by the patterns are adjustable and are obtained by using suitable programmed hydraulic control and driving means. 